In a long term evolution (LTE) system, when data sent by user equipment (UE) cannot be properly received by a serving base station, the UE performs uplink retransmission, where each retransmission time is about 8 ms. When the UE is on an edge of a cell, because of limited transmit power of the UE, the UE may need to perform uplink retransmission for multiple times to ensure that the serving base station can properly receive the data. Therefore, the data may undergo a quite long delay, which greatly affects user experience.
To resolve the foregoing problem, in uplink data transmission, transmission time interval bundling (TTI Bundling) is introduced, that is, a base station configures an uplink TTI Bundling function for UE. Therefore, each time the UE uses a physical uplink shared channel (Physical Uplink Shared Channel, PUSCH) to transmit uplink data, the UE transmits the uplink data for four times in four consecutive transmission time intervals (transmission time interval, TTI). The base station feeds back an acknowledgement (ACK) or a negative acknowledgement (NACK) only at a moment corresponding to the last TTI of the four TTIs in the bundling transmission. If a NACK is fed back, the UE is triggered to continue to retransmit the uplink data, so as to ensure quality of the uplink data transmission and reduce a delay, thereby improving user experience.
In the foregoing data transmission mode of TTI Bundling, only a transmission process of PUSCH uplink data is considered. However, in transmission processes of various types of other uplink and downlink data, a problem of a delay and unreliable transmission also exists. For example, when there is important data to be transmitted in downlink, for example, when a handover of the UE occurs, the base station sends a handover command to the UE. If the UE cannot properly receive the handover command because signal quality is relatively poor, the base station needs to retransmit the handover command. In this case, because the base station cannot learn whether the UE has a Bundling capability in downlink, if the handover command is retransmitted according to a conventional technology, for example, according to a hybrid automatic repeat request (Hybrid Automatic Repeat Request, HARQ), the UE may be unable to properly receive the handover command due to the delay and the like, which causes a final handover failure of the UE.